1. Field of the Invention
The present invention relates to a projection type liquid crystal display for projecting a light modulated spatially in accordance with an image for displaying.
2. Description of the Related Art
As a projection type liquid crystal display used to appreciate images and so forth, a liquid crystal projector, for example, wherein a light from a light source is irradiated on a liquid crystal panel and spatially modulated and the light transmitted through the liquid crystal panel is projected onto a screen or the equivalent by a projection optical system to display an image, has been conventionally developed.
Projection type liquid crystal displays involve a single-panel mode display using a liquid crystal panel provided with three types of color filters, i.e., R (red), G (green) and B (blue) filters and a three-panel mode display wherein monochrome liquid panels are provided in optical paths for B, R and G, respectively.
The color projection type liquid crystal display using a single-panel mode has a simple structure and is small-sized, light-weight and inexpensive. It is, however, disadvantageous in realizing high luminance due to large amounts of absorption of light by color filters and in cooling. To deal with such disadvantages, a projection type liquid crystal display consisting of a single-panel mode which does not employ color filters has been developed. For example, Japanese Published Unexamined Patent Application No. 4-60538 which corresponds to U.S. Pat. No. 5,161,042 or "ASIA DISPLAY '95", page 887 discloses a single-panel mode color liquid crystal display which places a condensing microlens for every set of three pixels to face each other, in which three colors of B, R, and G are incident from different directions and condensed on respective lenses and that the outgoing lights are incident on pixels corresponding to the three colors of B, R, and G, respectively. In the color liquid crystal display of this type, the light incident on the region (i.e. the black matrix portion in which a thin film transistor, or TFT serving as a switching device for driving pixels) between pixels can be effectively utilized and actual aperture ratio increases, which allows high luminance.
FIG. 1 is a block diagram showing an example of a single-panel mode projection type liquid crystal display which does not employ color filters. The projection type liquid color display comprises a light source 101, a UV (ultraviolet)-IR (infrared) cut filter 102, a glass rod integrator 103, a relay lens 104 and a collimator lens 105. With this arrangement, when a white light is emitted from the light source 101, the ultraviolet and infrared of the white light are removed by the UV-IR cut filter 102. Thereafter, uniform illuminance distribution is obtained by the glass rod integrator 103 and, at the same time, the resultant light is transmitted by the relay lens 104 and the collimator lens 105 and is emitted as a parallel light with a predetermined width.
The projection type liquid crystal display also comprises a dichroic mirror 106 for selectively separating the parallel light emitted from the collimator lens 105 into three colors of B, R and G which are fundamental colors for color display and emitting the light, an incidence side polarizing plate 107 for linearly polarizing the lights of three colors of B, R and G separated by the dichroic mirror 106, respectively, a liquid crystal panel 108 for spatially modulating the lights of three colors of B, R and G which have been linearly polarized by the incidence side polarizing plate 107 in accordance with an image for displaying, an outgoing side polarizing plate 109 for transmitting only the light polarized in a predetermined direction among the lights spatially modulated by the liquid crystal panel 108 and a projection lens 110 for projecting the light transmitted by the outgoing side polarizing plate 109 onto the screen. The incidence side polarizing plate 107 and the liquid crystal panel 108 are located with predetermined distances from the dichroic mirror 106, respectively.
The dichroic mirror 106 includes three mirrors, that is, a mirror 106B for B, a mirror 106R for R and a mirror 106G for G for selectively reflecting the lights of three colors of B, R and G, respectively. The mirrors 106B, 106R and 106G include color adjustment and holding mechanisms (not shown) for setting incident angles of lights of respective colors of R, G, and B incident on the liquid crystal panel 108 from different directions, respectively.
In the projection type liquid crystal display as described above, the white light emitted from the light source 101 is separated into lights of three colors of R, G and B by the three dichroic mirrors 106R, 106G and 106G. The separated color lights are incident from different angles on the liquid panel 108 which is provided independently of the dichroic mirrors 106R, 106G and 106B.
FIG. 2 is a block diagram showing an example of a three-panel mode projection type liquid crystal display. The projection type liquid crystal display of this type comprises a light source 201 having the same function as in the single-panel mode projection type liquid crystal display shown in FIG. 1, a UV-IR cut filter 202, a glass rod integrator 203, a relay lens 204 and a collimator lens 205. A ray of white light from the light source 201 is transmitted by the collimator lens 205 and emitted as a parallel light.
The projection type liquid crystal display also comprises dichroic mirrors 206R, 206G and 206B, provided on the same optical path at predetermined intervals, for selectively separating the parallel light emitted from the collimator lens 205 into lights of three colors of R, G and B which are fundamental colors for color display, a reflection mirror 207 for further reflecting the light of color R reflected by the dichroic mirror 206R in a predetermined direction, a reflection mirror 208 for further reflecting the light of color B reflected by the dichroic mirror 206B in a predetermined direction, incidence side polarizing plates 209R, 209G and 209B for linearly polarizing the lights of three colors of R, G and B which have been separated by the dichroic mirrors 206R, 206G and 206B, respectively, monochrome liquid panels 210R, 210G and 210B for spatially modulating the lights of three colors of R, G and B which have been linearly polarized by the incidence side polarizing plates 209R, 209G and 209B, respectively, outgoing side polarizing plates 211R, 211G and 211B for transmitting only the light polarized in a predetermined direction among the lights spatially modulated by the liquid crystal panels 210R, 210G and 210B, a color synthesizing dichroic prism 212 for synthesizing the lights of three colors of R, G and B transmitted by the outgoing side polarizing plates 211R, 211G and 211B and a projection lens 213 for projecting the light synthesized by the color synthesizing dichroic prism 212 onto a screen 111.
The color synthesizing dichroic prism 212 is a cubical prism. The dichroic prism 212 has incidence surfaces 212R, 212G and 212B on which the lights of three colors of R, G and B are incident, respectively. The incidence side polarizing plate 209R, the liquid crystal panel 210R and the outgoing side polarizing plate 211R are arranged to face the incidence surface 212R of the color synthesizing dichroic prism 212. The incidence side polarizing plate 209G, the liquid crystal panel 210G and the outgoing side polarizing plate 211G are arranged to face the incidence plane 212G perpendicular to the incidence surface 212R of the dichroic prism 212. The incidence side polarizing plate 209B, the liquid crystal panel 210B and the outgoing side polarizing plate 211B are arranged to face the remaining incidence plane 212B parallel to the incidence surface 213R of the color synthesizing dichroic prism 212.
The incidence side polarizing plates 209R, 209G and 209B as well as the liquid crystal panels 210R, 210G and 210B are arranged at a distance from the dichroic mirror 212, respectively.
In the three-panel mode projection type liquid crystal display of this type, the lights of three colors of R, G and B separated by the dichroic mirrors 206R, 206G and 206B are linearly polarized by the incidence side polarizing plates 209R, 209G and 298B and then incident on the liquid crystal panels 210R, 210G and 210B through the air in the space, respectively. The lights emitted from the liquid crystal panels 210R, 210B and 210B are incident on the outgoing side polarizing plates 211R, 211G and 211B and the lights of three colors of R, G and B transmitted by the outgoing polarizing plates 211R, 211G and 211B are incident on the incident surfaces 212R, 212G and 212B of the color synthesizing dichroic prism 212 through the air in the space, respectively. The lights of three colors of R, G and B incident on the incident surfaces 212R, 212G and 212B of the color synthesizing dichroic prism 212 are color-synthesized by the action of the color synthesizing dichroic prism 212 and thereafter projected onto the screen 111 through the projection lens 213.
The projection type liquid crystal displays of these various types as described above have the following disadvantages. Since the liquid crystal panels are arranged to be completely separated from other optical components such as dichroic mirrors, contaminants such as dusts and dirt are easily attached to the surfaces of the liquid panels, resulting in a deterioration in image quality and a decrease in light quantity. Due to the separate arrangement of the liquid panels from their peripheral optical components, simple structure cannot be sufficiently realized.
Furthermore, in the above-stated various types of projection type liquid crystal displays, to keep off the heat generated from the liquid panels, cooling fans (not shown) are usually provided to blow airs to thereby cool the crystal panels. As described above, however, the liquid crystal panels are separately arranged from other optical components and the surfaces thereof come into contact with the air of low heat conductivity. Due to this, the cooling effect of the cooling fans are lowered, which adversely affects image quality. To improve the cooling effect, it is necessary to increase the rotation rate of the cooling fans, If so, however, noises are produced unnecessarily by the cooling fans themselves as well as the blow from the fans.
In the single-panel mode projection type liquid crystal display as shown in FIG. 1, in particular, it is required to keep spaces corresponding to the thicknesses of the three dichroic mirrors 106B, 106R and 106G and color adjustment and holding mechanisms for setting incident angles of lights of respective colors of R, G and B incident on the liquid crystal panel 108 in different directions. This arrangement disadvantageously provides a large-sized structure. Besides, due to irregular thickness in the three dichroic mirrors 106B, 106R and 106G produced in manufacturing process, it is difficult to dispense with the adjustment of incident angles and to expect the satisfactory accuracy of the reflection angle. Additionally, contaminants such as dust and dirt are easily attached to the front and rear surfaces of the three dichroic mirrors 106B, 106R and 106G, resulting in a deterioration in image quality and a decrease in light quantity. Mixture of colors occurs due to stray lights reflected on the rear surfaces of the dichroic mirrors 106B, 106R and 106G, thereby lowering image quality.
In the three-panel mode projection type liquid crystal display as shown in FIG. 2, in particular, the color synthesizing dichroic prism 212 is separately provided from other optical components and clearances are given in the spaces of the incidence surfaces 212R, 212G and 212B, respectively. Owing to this, contaminants such as dust and dirt are easily attached to the incidence surfaces 212R, 212G and 212B, thereby resulting in a deterioration in image quality and a decrease in light quantity. In addition, the lights reflected on the incidence surfaces 212R, 212G and 212B become stray lights to thereby deteriorate image quality.